Striking increases in expression of the cysteine protease cathepsin B are present in a wide variety of human cancers. Expression is evaluated early in tumorigenesis, appearing in premalignant lesions in human prostate and esophagus and prior to the amplification of the cathepsin B gene observed in esophageal carcinoma. The investigator's overall hypothesis is that aberrant regulation of cathepsin B expression contributes to tumor progression. In Aim 1, the investigator will test this hypothesis, using both in vitro and in vivo model systems to evaluate malignant phenotype, by: a) upregulating cathepsin B expression in Seg-1 human esophageal carcinoma cells which do not express cathepsin B, and b) downregulating cathepsin B expression in esophageal and prostate carcinoma and glioma cells which do express cathepsin B. In Aim 2, the investigator will analyze whether transcriptional mechanisms contribute to increases in cathepsin B expression in human esophageal and prostate carcinoma and glioma cell lines and thereby malignant progression. A spectrum of techniques will be used to identify novel (and known) transcription factors: yeast 1-hybrid, phage display, biochemical/mass spectroscopic, immunochemistry. The investigator will then use antisense and dominant negative approaches to modulate the expression of selected transcription factors (and that of cathepsin B) and test for subsequent effects on the malignant phenotype. In Aim 3, the investigator will analyze whether regulation of cathepsin B expression at the levels of alternative splicing and gene amplification contributes to increased cathepsin B expression and thereby malignant progression. The investigator will use Taqman to identify and quantitate transcript variants and Southerns to determine whether the cathepsin B gene is amplified, in both cases using microdissected human esophageal and prostate carcinomas and gliomas that cover the spectrum of tumor progression or come from various regions within the tumor. The investigator will transfect selected cathepsin B transcripts and co-amplify expression of cathepsin B in Seg-1 esophageal carcinoma cells which do not express cathepsin B and analyze for subsequent effects on malignant phenotype. These studies will identify molecular mechanisms for modulating the expression of cathepsin B as well as add to our general knowledge of how changes in transcriptional complexes, alternative splicing and gene amplification of tumors are related to the progression of these tumors.